This paper is devoted to the description of procedures used in our IR/RAMAN spectrum simulation system. Based on substructure/subspectrum correlations established between linked databases. The search is performed in the following order; small molecules/specific fragments/atom centered FRELs(FREL;Fragment centered on an Environment which is Limited)/bond focused FRELs. Comparative study with several reported methods has been carried out to show good performance of this software both for IR and RAMAN spectrum simulation.